Enthralled scientists spot a giant tortoise behaving in a strange, wild way

Biologists on Frégate Island, east of Africa, spotted a giant tortoise acting strangely in July 2020. They grabbed a camera and started filming.

The giant female tortoise lumbered towards a small bird (a tern chick) who was standing on a log. The tortoise, who typically devours plants on the island, opened its mouth wide. The bird ran away, down the log. But the tortoise pursued.

"At the end of the log the chick stopped retreating, enabling the tortoise to close its jaws directly on the head of the chick," the researchers wrote. "The chick, now dead, was dropped and the tortoise had to climb off the log to retrieve it. Once retrieved, the chick was swallowed whole."

The footage of this wild event is the first known documentation of a giant tortoise (who largely devours plants) hunting and eating another animal, though people have reported (but not recorded) this behavior before. The evidence of the attack is compelling for a number of reasons, not least because it underscores how our understanding of nature is still evolving, and challenges assumptions about how animals live.

"It changes the way most people think about tortoises," Justin Gerlach, a biologist at the University of Cambridge, told Mashable. Gerlach is a giant tortoise researcher and an author of the newly published study in the scientific journal Current Biology. There's more to them than we think, he said.

"It also shows that you can still make unexpected discoveries by observation," Gerlach added.

"The more we watch, the more we learn," agreed Rob Baldwin, a conservation biologist at Clemson University who researches reptiles. "These animals have lives. Their lives are secret from us, unless we watch them. That's why having biologists and professionals out in the field is so important." Baldwin had no role in the research.

Based on the rare footage, there's little doubt the female tortoise was hunting, as opposed to opportunistically snagging a nearby piece of protein. Gerlach and Anna Zora, a conservationist on Frégate Island who filmed the remarkable event, concluded the tortoise acted deliberately to attack the young tern. "It's seen the bird from a distance and goes straight at it," explained Gerlach. "Normally [giant tortoises] are slower and less directed. It clearly has purpose."

The images and video below show the methodical hunt, which Baldwin also noted was clearly systematic.

Images of the giant tortoise attacking the tern on Frégate Island. Credit: Anna Zora

Reptiles, often living amid vegetation or under rocks, can be challenging to observe. On top of that, we're still learning about how creatures like giant tortoises truly live because humanity decimated their populations. Today, their numbers and conditions are returning to more normal, natural states.

"This is a group of animals that has long been persecuted," explained Baldwin, noting they were once rounded up and stored as food on ships. On Frégate Island, conservationists bred the current population of 3,000 giant Aldabra tortoises from just 150 tortoises, according to the private island's website.

As the island's habitat is restored, the wilds are returning (aka "rewilding"), including some 265,000 noddy terns that have recolonized the island. With rewilding comes the return of animal behavior little seen before, or never seen, by today's scientists — like a tortoise hunting a tern. "We don't know whether this is a totally new behavior or one that has re-developed," said Gerlach. "Personally, I think it's the latter, showing that where we restore natural systems we may recreate old species interactions, allowing things that no human has seen."

As biologists continue observing life on Frégate Island, they may discover these tortoises do indeed more regularly eat birds and have a genuinely mixed diet. Many tortoises could be expert hunters, too. We'll see what the wilderness has in store.

Rewilding doesn't just bring back life. It invites surprises.